1. Field of the Invention
In general, the present invention relates to workholding and fixturing devices for holding parts, and more particularly, to fixturing devices for holding parts in coordinate measuring machines and other apparatuses.
2. Description of Related Art
Coordinate measuring machines (CMMs) are precision instruments used to measure the physical, geometrical properties of items. A CMM usually includes a work surface with a grid of threaded holes at a defined, regular pitch for fixturing parts, and a mechanism that actually takes the measurements. The typical mechanism in a CMM is a “bridge”-type arrangement that suspends a probe over the work surface in such a way that the probe can move in three axes. The probe may be a mechanical contact probe or a non-contact probe.
As one example, CMMs are used for quality control in manufacturing. A manufactured part, like a mating bracket, would be fixed and lightly clamped to the work surface using any number of fixtures. The machine would then take the necessary dimensional measurements.
A CMM fixture for holding a part during measurement may include any number of fixturing elements and any number of locating elements. Fixturing elements primarily provide physical support or clamping for the part; locating elements are provided in order to precisely locate or place a part for measurement. One type of locating element is a standoff pin, which can be inserted into a particular hole or opening in a part to locate it precisely.
Each part may present unique fixturing challenges. However, there are some common issues that arise in fixturing. For example, the fixed pitch of the work surface attachment grid can pose problems when none of the grid positions on the work surface would place a fixturing or locating element in the desired position to constrain the part for measurement. Locating or fixturing elements that attach to the work surface at one or several points and provide a sliding track can be used, but these elements are often expensive, small, and can be cumbersome to use.